There is a continuing need for a low cost method of forming a single casting or a relatively few castings such as may be required for prototype parts or for very low volume production. There have been developed a number of prototype-making processes that yield plastic parts or synthetic resin-coated aggregate parts that are built up, section by section, by a controlled scanning laser beam that polymerizes a layer of molten plastic or fuses a layer of polymeric film coated aggregate particles. However, there is no low cost method for making a single mold or relatively few molds for making a few cast metal parts.
As stated, it is known to coat ceramic particles or sand particles, glass beads or the like with a suitable fusible polymer film for the purpose of building a prototype part of such materials. In this practice, a flat surface is usually dusted or coated with a number of such particles, and a computer-controlled laser beam sweeps back and forth over the particles selectively heating those that are to be fused together to constitute a particular layer or planar section of the part to be fused together. The work surface or stage carrying the flat section is then lowered by the thickness of a particle layer, a new layer of particles applied, and the process of fusing the new layer of particles with the laser beam is repeated. In this way of forming successive layers of bonded particles or polymerized monomers, virtually any shape of a prototype part can be formed. However, the part is representative only of the shape of the adhesive bound particles and cannot represent all properties of a desired cast metal part. Furthermore, such prior art prototypes could not be used as casting patterns because they were not strong enough to form a two-part mold around them and they could not be easily removed from such a mold.
It is an object of this invention to provide a method of making a pattern and mold for the production of one or a few metal castings.